Catheters for use in penetrating various passages in the human body for various procedures are well known in the prior art. Uses for such catheters include: penetrating cardiac blood vessels; penetrating cerebral blood vessels; and penetrating the uterus in embryo implant procedures, for example. Catheters used in the aforesaid procedures all include a distal end which penetrates the body passages, and a proximal end which remains outside of the body and is used to manually "steer" the distal end of the catheter through the body passages. The aforesaid catheters are typically inserted into the body through the bore of a proximal catheter guide cannula which penetrates the body. Once the guide cannula penetrates the body passage in question, the catheter is advanced into the body passage through the guide cannula.
In order to avoid damaging delicate body tissues, the distal tip of the catheter should be formed from a soft material. U.S. Pat. No. 4,531,943, Van Tassel et al; U.S. Pat. No. 4,863,442, DeMello et al; U.S. Pat. No. 4,886,506, Lovgren et al; U.S. Pat. No. 5,045,072, Castillo et al; U.S. Pat. No. 5,221,270, Parker; U.S. Pat. No. 5,234,416, Macaulay et al; U.S. Pat. No. 5,571,073, Castillo; U.S. Pat. No. 5,769,830, Parker; and U.S. Pat. No. 5,792,124, Horrigan et al all describe catheters that are provided with soft distal ends so as to avoid tissue damage when inserted into the body. The prior art also recognizes the fact that while the distal end of the catheter should be soft, more proximal portions of the catheter should preferably be more rigid in order to facilitate pushing of the catheter into the body through the guide cannula. The aforesaid patents all disclose catheter structures which are provided with a soft distal tip and a more rigid proximal portion. In each case, the softer distal tip portion of the catheter is a separate element which is attached to the stiffer proximal portion, and the stiffer proximal portion is typically reinforced with a stiffener, such as a braid or the like. The prior art catheters described in the above-identified patents are thus complex structures and require assembly.
Another approach to the production of a soft distal tip catheter which has been proposed is a catheter wherein both the distal and proximal portions of the catheter are formed from the same soft material. This type of catheter avoids the complexity of the aforesaid patented catheters and also avoids the need to assemble the distal and proximal catheter portions, however, this approach produces a catheter that is difficult to steer through the guide cannula due to the tendency of the proximal portion of the catheter to flex or wobble when the physician attempts to push the catheter into the subject's body through the guide cannula. This problem requires a second attendant, typically a nurse, to try to manually prevent the catheter from flexing as the physician advances the catheter into the body.
The aforesaid problem of catheter flexure, or wobble, is particularly troublesome in the field of implanting of embryo into a female's womb. This problem may be the result of the cervical constriction which is encountered by a physician during the implant procedure. When an embryo is implanted in a female's uterus, the guide cannula will be advanced into the os of the cervix. During insertion of the guide cannula, the embryo implant catheter will be retracted completely inside of the guide cannula so as to protect the embryo. Once the guide cannula is in position in the cervix os, the inner catheter, the distal tip of which holds the embryo to be implanted, is then advanced through the guide cannula and through the cervix and into the uterus. Thus, a catheter which is formed solely from a soft material will be difficult to insert into the womb due to the cervical constriction adjacent to the cervical os.
It would be highly desirable to provide a catheter, particularly an embryo implant catheter, which has a soft distal tip and also has a stiffer proximal portion, which catheter does not require assembly, and is formed from a homogeneous material.